An inkjet recording apparatus is configured to print an image through inkjet recording to thereby realize high quality imaging at relatively low cost. With the widespread use of the personal computer, the inkjet recording apparatus is becoming commonly used as a color image output apparatus for the personal computer.
An inkjet recording head used in such an inkjet recording apparatus has plural nozzles arranged in the sub scanning direction (i.e., traveling direction of recording paper), and is moved in the main scanning direction (i.e., direction perpendicular to the traveling direction of recording paper) by a carriage mechanism. The nozzles of the inkjet recording head are configured to discharge ink droplets at appropriate timings according to dot pattern data obtained by developing print data. In this way, the ink droplets discharged from the nozzles are adhered to recording paper to thereby realize image printing.
As is described above, the inkjet recording apparatus may be used as an output apparatus of a personal computer. In this respect, techniques for increasing the recording speed, improving the image quality, reducing the apparatus size, and reducing the apparatus cost are in demand. It is noted that speed increase may be realized by increasing the ink discharge drive frequency, increasing the number of nozzles, or printing at a lower resolution in a case where the printing resolution is higher than the nozzle resolution, for example. Image quality improvement may be realized by miniaturizing the nozzles or increasing the printing resolution, for example.
In order to realize speed increase and image quality improvement at the same time, the number of nozzles may be increased to realize high resolution printing with small dots. However, it is noted that by increasing the number of nozzles, the size of the inkjet recording head is increased to thereby cause cost increase. Also, it is noted that an increase in the size of the recording head may lead to an increase in the overall size of the inkjet recording apparatus, an increase in the amount of vibrations and noise upon moving the recording head, and an increase in the power consumption amount, for example. As can be appreciated from the above descriptions, speed increase and image quality improvement are in a tradeoff relationship.
In this respect, use of a technique that involves superficially increasing the resolution by adjusting the arrangement of nozzles is being proposed (e.g., see Japanese Laid-Open Patent Publication No. 2-26753, Japanese Patent No. 3,533,771, and Japanese Laid-Open Patent Publication No. 2001-260423). It is noted that this technique has been developed in view of the demand for higher resolution and the fact that monochrome printing is generally used more often than color printing. According to this technique, nozzles of the three primary colors (magenta, cyan, yellow) are arranged on the same scanning lines that are shifted from the positions of black nozzles by ½ the nozzle pitch. With such an arrangement, in the case of performing monochrome image printing, black realized by black ink and composite black realized by combining the three primary color inks may be used for printing a monochrome image so that the printing resolution for monochrome image printing may be double the printing resolution for color image printing without causing a decrease in the printing speed.
Also, in order to miniaturize the head size and increase the nozzle density, two rows of nozzles may be staggered with respect to each other. Such a nozzle arrangement is particularly applied to a piezoelectric recording head, which has relatively large piezoelectric elements so that densification of the nozzles is highly demanded.
According to the technique disclosed in the above-cited documents, composite black is used in addition to black from black ink, and the three primary color nozzles are arranged on the same scanning lines while the black ink nozzles are shifted by ½ the nozzle pitch from the scanning line positions of the primary color nozzles. Therefore, the technique of staggering the nozzles of one nozzle row with respect to the nozzles of another nozzle row to increase the nozzle density and miniaturize the head size may not be combined with the above technique for realizing high quality imaging at high speed. In other words, nozzle densification/head miniaturization and high-quality/high-speed printing cannot be realized at the same time based on the above-described techniques.